The present invention relates to an exhaust gas purifying system for a multi-cylinder internal combustion engine, of a type in which pulsations of the exhaust gas pressure are used to induce atmospheric air into the exhaust passageway of the engine.
As is well known in the art, internal combustion engines are provided with exhaust gas purifying systems which feed into exhaust passageways of the engines secondary air for burning or oxidizing noxious burnable components present in the exhaust gases from the engine, by means of a negative pressure of a pulsation of the exhaust gas pressure produced in exhaust passageways and/or so called ejector effect of the engine exhaust gases.
For supplying a sufficient amount of secondary air to support the burning of the noxious components in the exhaust passageway, the exhaust gas purifying system of the foregoing type requires the provision of numerous air supply tubes due to the relatively low flow rate of secondary air induced through each of the tubes. The provision of these numerous tubes makes the system complex in its structure and space-taking in itself, which inevitably involves skillful and meticulous installation work and high production cost.
The conventional exhaust gas purifying system further encounters a drawback, due to the requirement of the provision of the numerous secondary air supply tubes, that the secondary air supplied to the exhaust passageway is likely to be admixed with the mass of the exhaust gases to be recirculated through an exhaust gas recirculation passageway, which causes to diverge from a predetermined value the air/fuel ratio of the air/fuel mixture to be supplied to the engine and therefore causes unstable operation and high fuel consumption of the engine.
In addition to the above, such admixture of the secondary air with the recirculated exhaust gases causes an increase of the combustion temperature in the engine cylinder thus resulting in the reduced emission control effect of the system with respect to the formation of oxides of nitrogen.